This usually happens with long hair, because ends don’t get enough scalp oil. It gets worse after using too much of hair dryers, hair coloring and curling.
Taking care of such hair requires both products for oily scalp and dry hair. The way to wash such hair will be this. First using shampoo for dry hair wash hair without touching the scalp. Then using shampoo for oily scalp wash roots with light massage. After shampooing apply a caring product for ends (more about caring products). Also before shampooing mixed type hair you can put osmo protection to ends like it is done for dry hair. More about osmo protection.